Load control device for use with lighting circuits having three-way switches

ABSTRACT

A smart dimmer for control of a lighting load from an AC power source can replace any switch in a three-way or four-way lighting control system. The smart dimmer can be connected on the line-side or the load-side of a three-way system with a standard three-way switch in the other location. According to one embodiment of the present invention, the dimmer includes two triacs to control the intensity of the connected lighting load. The dimmer preferably includes two gate drive circuits coupled to the gates of the triacs for rendering the triacs conductive each half-cycle of the AC power source. The gate drive circuits include sensing circuits for detect whether the gates currents are flowing after the triacs are rendered conductive. A controller is operable to determine the state of the lighting load in response to whether the gate current is flowing or not flowing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of commonly-assignedco-pending U.S. patent application Ser. No. 11/767,279, filed Jun. 22,2007, entitled LOAD CONTROL DEVICE FOR USE WITH LIGHTING CIRCUITS HAVINGTHREE-WAY SWITCHES, which is a continuation-in-part of commonly-assignedco-pending U.S. patent application Ser. No. 11/447,496, filed Jun. 6,2006, entitled DIMMER SWITCH FOR USE WITH LIGHTING CIRCUITS HAVINGTHREE-WAY SWITCHES, which claims priority from commonly-assigned U.S.Provisional Application Ser. No. 60/687,690, filed Jun. 6, 2005,entitled INTELLIGENT THREE-WAY AND FOUR-WAY DIMMERS. The entiredisclosures of all applications are hereby incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to load control devices for electricalwiring systems having three-way switches. In particular, the presentinvention relates to a dimmer switch that can be substituted for afour-way switch, a line-side three-way switch, or a load-side three-wayswitch in lighting circuits having either two or more points of control,such as, for example, a four-way system.

2. Description of the Related Art

Three-way and four-way switch systems for use in controlling loads inbuildings, such as lighting loads, are known in the art. Typically, theswitches used in these systems are wired to the building'salternating-current (AC) wiring system, are subjected to AC sourcevoltage, and carry full load current, as opposed to low-voltage switchsystems that operate at low voltage and low current, and communicatedigital commands (usually low-voltage logic levels) to a remotecontroller that controls the level of AC power delivered to the load inresponse to the commands. Thus, as used herein, the terms “three-wayswitch”, “three-way system”, “four-way switch”, and “four-way system”mean such switches and systems that are subjected to the AC sourcevoltage and carry the full load current.

A three-way switch derives its name from the fact that it has threeterminals and is more commonly known as a single-pole double-throw(SPDT) switch, but will be referred to herein as a “three-way switch”.Note that in some countries a three-way switch as described above isknown as a “two-way switch”.

A four-way switch is a double-pole double-throw (DPDT) switch that iswired internally for polarity-reversal applications. A four-way switchis commonly called an intermediate switch, but will be referred toherein as a “four-way switch”.

In a typical, prior art three-way switch system, two three-way switchescontrol a single load, and each switch is fully operable toindependently control the load, irrespective of the status of the otherswitch. In such a system, one three-way switch must be wired at the ACsource side of the system (sometimes called “line side”), and the otherthree-way switch must be wired at the load side of the system.

FIG. 1A shows a standard three-way switch system 100, which includes twothree-way switches 102, 104. The switches 102, 104 are connected betweenan AC voltage source 106 and a lighting load 108. The three-way switches102, 104 each include “movable” (or common) contacts, which areelectrically connected to the AC voltage source 106 and the lightingload 108, respectively. The three-way switches 102, 104 also eachinclude two fixed contacts. When the movable contacts are making contactwith the upper fixed contacts, the three-way switches 102, 104 are inposition A in FIG. 1A. When the movable contacts are making contact withthe lower fixed contact, the three-way switches 102, 104 are in positionB. When the three-way switches 102, 104 are both in position A (or bothin position B), the circuit of system 100 is complete and the lightingload 108 is energized. When switch 102 is in position A and switch 104is in position B (or vice versa), the circuit is not complete and thelighting load 108 is not energized.

Three-way dimmer switches that replace three-way switches are known inthe art. An example of a three-way dimmer switch system 150, includingone prior art three-way dimmer switch 152 and one three-way switch 104is shown in FIG. 1B. The three-way dimmer switch 152 includes a dimmercircuit 152A and a three-way switch 152B. A typical, AC phase-controldimmer circuit 152A regulates the amount of energy supplied to thelighting load 108 by conducting for some portion of each half-cycle ofthe AC waveform, and not conducting for the remainder of the half-cycle.Because the dimmer circuit 152A is in series with the lighting load 108,the longer the dimmer circuit conducts, the more energy will bedelivered to the lighting load 108. Where the lighting load 108 is alamp, the more energy that is delivered to the lighting load 108, thegreater the light intensity level of the lamp. In a typical dimmingoperation, a user may adjust a control to set the light intensity levelof the lamp to a desired light intensity level. The portion of eachhalf-cycle for which the dimmer conducts is based on the selected lightintensity level. The user is able to dim and toggle the lighting load108 from the three-way dimmer switch 152 and is only able to toggle thelighting load from the three-way switch 104. Since two dimmer circuitscannot be wired in series, the three-way dimmer switch system 150 canonly include one three-way dimmer switch 152, which can be located oneither the line side or the load side of the system.

A four-way switch system is required when there are more than two switchlocations from which to control the load. For example, a four-way systemrequires two three-way switches and one four-way switch, wired in wellknown fashion, so as to render each switch fully operable toindependently control the load irrespective of the status of any otherswitches in the system. In the four-way system, the four-way switch isrequired to be wired between the two three-way switches in order for allswitches to operate independently, i.e., one three-way switch must bewired at the AC source side of the system, the other three-way switchmust be wired at the load side of the system, and the four-way switchmust be electrically situated between the two three-way switches.

FIG. 1C shows a prior art four-way switching system 180. The system 180includes two three-way switches 102, 104 and a four-way switch 185. Thefour-way switch 185 has two states. In the first state, node A1 isconnected to node A2 and node B1 is connected to node B2. When thefour-way switch 185 is toggled, the switch changes to the second statein which the paths are now crossed (i.e., node A1 is connected to nodeB2 and node B1 is connected to node A2). Note that a four-way switch canfunction as a three-way switch if one terminal is simply not connected.

FIG. 1D shows another prior art switching system 190 containing aplurality of four-way switches 185. As shown, any number of four-wayswitches can be included between the three-way switches 102, 104 toenable multiple location control of the lighting load 108.

Multiple location dimming systems employing a smart dimmer switch and aspecially designed remote (or “accessory”) switch that permit thedimming level to be adjusted from multiple locations have beendeveloped. A smart dimmer is one that includes a microcontroller orother processing means for providing an advanced set of control featuresand feedback options to the end user. For example, the advanced featuresof a smart dimmer may include a protected or locked lighting preset,fading, and double-tap to full intensity. To power the microcontroller,smart dimmers include power supplies, which draw a small amount ofcurrent through the lighting load each half-cycle when the semiconductorswitch is non-conducting. The power supply typically uses this smallamount of current to charge a storage capacitor and develop adirect-current (DC) voltage to power the microcontroller. An example ofa multiple location lighting control system, including a wall-mountablesmart dimmer switch and wall-mountable remote switches for wiring at alllocations of a multiple location dimming system, is disclosed incommonly assigned U.S. Pat. No. 5,248,919, issued on Sep. 28, 1993,entitled LIGHTING CONTROL DEVICE, which is herein incorporated byreference in its entirety.

Referring again to the system 150 of FIG. 1B, since no load currentflows through the dimmer circuit 152A of the three-way dimmer switch 152when the circuit between the supply 106 and the lighting load 108 isbroken by either three-way switch 152B or 104, the dimmer switch 152 isnot able to include a power supply and a microcontroller. Thus, thedimmer switch 152 is not able to provide the advanced set of features ofa smart dimmer to the end user.

FIG. 2 shows an example multiple location lighting control system 200including one wall-mountable smart dimmer switch 202 and onewall-mountable remote switch 204. The dimmer switch 202 has a Hot (H)terminal for receipt of an AC source voltage provided by an AC powersupply 206, and a Dimmed Hot (DH) terminal for providing a dimmed-hot(or phase-controlled) voltage to a lighting load 208. The remote switch204 is connected in series with the DH terminal of the dimmer switch 202and the lighting load 208, and passes the dimmed-hot voltage through tothe lighting load 208.

The dimmer switch 202 and the remote switch 204 both have actuators toallow for raising, lowering, and toggling on/off the light intensitylevel of the lighting load 208. The dimmer switch 202 is responsive toactuation of any of these actuators to alter the dimming level (or powerthe lighting load 208 on/off) accordingly. In particular, actuation ofan actuator at the remote switch 204 causes an AC control signal, orpartially rectified AC control signal, to be communicated from thatremote switch 204 to the dimmer switch 202 over the wiring between theAccessory Dimmer (AD) terminal of the remote switch 204 and the ADterminal of the dimmer switch 202. The dimmer switch 202 is responsiveto receipt of the control signal to alter the dimming level or togglethe load 208 on/off. Thus, the load can be fully controlled from theremote switch 204.

The user interface of the dimmer switch 202 of the multiple locationlighting control system 200 is shown in FIG. 3. As shown, the dimmerswitch 202 may include a faceplate 310, a bezel 312, an intensityselection actuator 314 for selecting a desired level of light intensityof a lighting load 208 controlled by the dimmer switch 202, and acontrol switch actuator 316. The faceplate 310 need not be limited toany specific form, and is preferably of a type adapted to be mounted toa conventional wall-box commonly used in the installation of lightingcontrol devices. Likewise, the bezel 312 and the actuators 314, 316 arenot limited to any specific form, and may be of any suitable design thatpermits manual actuation by a user.

An actuation of the upper portion 314A of the actuator 314 increases orraises the light intensity of the lighting load 208, while an actuationof the lower portion 314B of the actuator 314 decreases or lowers thelight intensity. The actuator 314 may control a rocker switch, twoseparate push switches, or the like. The actuator 316 may control a pushswitch, though the actuator 316 may be a touch-sensitive membrane. Theactuators 314, 316 may be linked to the corresponding switches in anyconvenient manner. The switches controlled by actuators 314, 316 may bedirectly wired into the control circuitry to be described below, or maybe linked by an extended wired link, infrared (IR) link, radio frequency(RF) link, power line carrier (PLC) link, or otherwise to the controlcircuitry.

The dimmer switch 202 may also include an intensity level indicator inthe form of a plurality of light sources 318, such as light-emittingdiodes (LEDs). Light sources 318 may be arranged in an array (such as alinear array as shown) representative of a range of light intensitylevels of the lighting load 208 being controlled. The intensity levelsof the lighting load 208 may range from a minimum intensity level, whichis preferably the lowest visible intensity, but which may be “full off”,or zero, to a maximum intensity level, which is typically “full on”, orsubstantially 100%. Light intensity level is typically expressed as apercent of full intensity. Thus, when the lighting load 208 is on, lightintensity level may range from 1% to substantially 100%.

A simplified block diagram of the dimmer switch 202 and the remoteswitch 204 of the multiple location lighting control system 200 is shownin FIG. 4. The dimmer switch 202 employs a semiconductor switch 420coupled between the hot terminal H and the dimmed hot terminal DH, tocontrol the current through, and thus the light intensity of, thelighting load 208. The semiconductor switch 420 may be implemented as atriac or two field effect transistors (FETs) in anti-series connection.The semiconductor switch 420 has a control input (or gate), which isconnected to a gate drive circuit 424. The input to the gate will renderthe semiconductor switch 420 conductive or non-conductive, which in turncontrols the power supplied to the lighting load 208. The gate drivecircuit 424 provides control inputs to the semiconductor switch 420 inresponse to command signals from a microcontroller 426.

The microcontroller 426 generates command signals to a visual display,e.g., a plurality of LEDs 418, for feedback to the user of the dimmerswitch 202. The microcontroller 426 receives inputs from a zero-crossingdetector 430 and a signal detector 432. A power supply 428 generates aDC output voltage V_(CC) to power the microcontroller 426. The powersupply is coupled between the hot terminal H and the dimmed hot terminalDH.

The zero-crossing detector 430 determines the zero-crossings of theinput AC waveform from the AC power supply 206. A zero-crossing isdefined as the time at which the AC supply voltage transitions frompositive to negative polarity, or from negative to positive polarity, atthe beginning of each half-cycle. The zero-crossing information isprovided as an input to microcontroller 426. The microcontroller 426provides the gate control signals to operate the semiconductor switch420 to provide voltage from the AC power supply 206 to the lighting load208 at predetermined times relative to the zero-crossing points of theAC waveform.

Generally, two techniques are used for controlling the power supplied tothe lighting load 208: forward phase control dimming and reverse phasecontrol dimming. In forward phase control dimming, the semiconductorswitch 420 is turned on at some point within each AC line voltagehalf-cycle and remains on until the next voltage zero-crossing. Forwardphase control dimming is often used to control energy to a resistive orinductive load, which may include, for example, a magnetic low-voltagetransformer or an incandescent lamp. In reverse phase control dimming,the semiconductor switch 420 is turned on at the zero-crossing of the ACline voltage and turned off at some point within each half-cycle of theAC line voltage. Reverse phase control is often used to control energyto a capacitive load, which may include, for example, an electroniclow-voltage transformer. Since the semiconductor switch 420 must beconductive at the beginning of the half-cycle, and be able to be turnedoff with in the half-cycle, reverse phase control dimming requires thatthe dimmer have two FETs in anti-serial connection, or the like.

The signal detector 432 has an input 440 for receiving switch closuresignals from momentary switches T, R, and L. Switch T corresponds to atoggle switch controlled by the switch actuator 316, and switches R andL correspond to the raise and lower switches controlled by the upperportion 314A and the lower portion 314B, respectively, of the intensityselection actuator 314.

Closure of switch T will connect the input of the signal detector 432 tothe DH terminal of the dimmer switch 202, and will allow both positiveand negative half-cycles of the AC current to flow through the signaldetector. Closure of switches R and L will also connect the input of thesignal detector 432 to the DH terminal. However, when switch R isclosed, current can only flow through the signal detector 432 during thepositive half-cycle of the AC power supply 406 because of a diode 434.In similar manner, when switch L is closed, current can only flowthrough the signal detector 432 during the negative half-cycles becauseof a diode 436. The signal detector 432 detects when the switches T, R,and L are closed, and provides two separate output signalsrepresentative of the state of the switches as inputs to themicrocontroller 426. A signal on the first output of the signal detector432 indicates a closure of switch R and a signal on the second outputindicates a closure of switch L. Simultaneous signals on both outputsrepresents a closure of switch T. The microprocessor controller 426determines the duration of closure in response to inputs from the signaldetector 432.

The remote switch 204 provides a means for controlling the dimmer switch202 from a remote location in a separate wall box. The remote switch 204includes a further set of momentary switches T′, R′, and L′ and diodes434′ and 436′. A wire connection is made between the AD terminal of theremote switch 204 and the AD terminal of the dimmer switch 202 to allowfor the communication of actuator presses at the remote switch. The ADterminal is connected to the input 440 of the signal detector 432. Theaction of switches T′, R′, and L′ in the remote switch 204 correspondsto the action of switches T, R, and L in the dimmer switch 202.

The system shown in FIGS. 2, 3, and 4 provides a fully functionalthree-way switching system wherein the user is able to access allfunctions, such as, for example, dimming at both locations. However, inorder to provide this functionality, both switching devices need to bereplaced with the respective devices 202, 204.

Sometimes it is desired to place only one smart switch in the three-wayor four-way switching circuit. As shown in FIG. 1B, it is not possibleheretofore to do this by simply replacing the dimmer 152 with a smartdimmer, leaving mechanical three-way switch 104 in the circuit becausewhen switch 104 breaks the circuit, power no longer is provided to themicrocontroller of the smart dimmer (in place of the dimmer 152) becausecurrent no longer flows through the dimmer to the lighting load 108. Thethree-way and four-way dimmer switch according to the present inventionprovides a solution to this problem and also optionally provides a meansfor remote control of the switch.

In one prior art remote control lighting control system, a singlemulti-location dimmer and up to nine “accessory” dimmers can beinstalled on the same circuit to enable dimming from a plurality ofcontrols. In the prior art, accessory dimmers are necessary becauseprior art multi-location dimmers are incompatible with mechanicalthree-way switches. Accessory dimmers installed throughout a house cangreatly increase the cost of the components and of the installation of adimming system.

Moreover, even though the multiple location lighting control system 200allows for the use of a smart dimmer switch in a three-way system, it isnecessary for the customer to purchase the remote switch 204 along withthe smart dimmer switch 202. Often, the typical customer is unaware thata remote switch is required when buying a smart dimmer switch for athree-way or four-way system until after the time of purchase when thesmart dimmer switch is installed and it is discovered that the smartdimmer switch will not work properly with the existing mechanicalthree-way or four-way switch. Therefore, there exists a need for a smartdimmer that may be installed in any location of a three-way or four-waysystem without the need to purchase and install a special remote switch.

A smart three-way switch has also been designed that operates with aconventional mechanical three-way switch, but that system requiresrewiring of the mechanical three-way switch in order to provide properthree-way operation from both locations. This is the subject of commonlyassigned U.S. patent application Ser. No. 11/125,045, filed May 9, 2005,entitled DIMMER FOR USE WITH A THREE-WAY SWITCH, which is incorporatedherein by reference in its entirety.

SUMMARY OF THE INVENTION

The present invention provides a load control device adapted to becoupled to a circuit including an AC power source, a load, and asingle-pole double-throw three-way switch. The load control devicecomprises: first, second, and third electrical load terminals, first andsecond controllably conductive devices, and a controller. The first andsecond controllably conductive devices each have a conductive state anda non-conductive state. The first controllably conductive device iselectrically coupled between the first load terminal and the second loadterminal such that when the first controllably conductive device is inthe conductive state and the load control device is coupled to thecircuit, a load current is operable to flow between the first loadterminal and the second load terminal. The second controllablyconductive device is electrically coupled between the first loadterminal and the third load terminal such that when the secondcontrollably conductive device is in the conductive state and the loadcontrol device is coupled to the circuit, the load current is operableto flow between the first load terminal and the third load terminal. Thefirst and second controllably conductive devices have first and secondcontrol inputs, respectively, and are operable to enter the conductivestate in response to first and second gate currents conducted throughthe first and second control inputs. The controller is operable tocontrol the first and second controllably conductive devices to controlthe load between an on state and an off state. The controller operableto drive the first controllably conductive device to change the firstcontrollably conductive device from the non-conductive state to theconductive state each half-cycle of the AC line voltage. The controlleris operable to determine, in response to the magnitude of the first gatecurrent through the first control input of the first controllablyconductive device, whether the first controllably conductive device ispresently conducting current to the load.

The present invention further provides a method for controlling a loadin a circuit comprising a power source, the load, a load control device,and a single-pole double-throw three-way switch. The method comprisesthe steps of: (1) providing first, second, and third electrical loadterminals on the dimmer switch; (2) electrically coupling a firstcontrollably conductive device between the first load terminal and thesecond load terminal, the first controllably conductive device having aconductive state and a non-conductive, the first controllably conductivedevice arranged such that when the first controllably conductive deviceis in the conductive state, a load current is operable to flow betweenthe first load terminal and the second load terminal, the firstcontrollably conductive device having a first control input; (3)conducting a first gate current through the first control input to causethe first controllably conductive device to enter the conductive state;(4) electrically coupling a second controllably conductive devicebetween the first load terminal and the third load terminal, the secondcontrollably conductive device having a conductive state and anon-conductive state, the second controllably conductive device arrangedsuch that when the second controllably conductive device is in theconductive state, the load current is operable to flow between the firstload terminal and the third load terminal, the second controllablyconductive device having a second control input; (5) conducting a secondgate current through the second control input to cause the secondcontrollably conductive device to enter the conductive state; (6)monitoring the first and second gate currents; and (7) determining, inresponse to the step of monitoring the first and second gate currents,whether the respective controllably conductive device is presentlyconducting the current to the load.

In addition, the present invention provides a load control system forcontrolling the amount of power delivered to an electrical load from anAC power source generating an AC line voltage. The load control systemcomprises a single-pole double-throw (SPDT) three-way switch and a loadcontrol device. The SPDT switch comprises a first fixed contact, asecond fixed contact, and a movable contact adapted to be coupled toeither the power source or the load. The SPDT three-way switch has afirst state in which the movable contact is contacting the first fixedcontact and a second state in which the movable contact is contactingthe second fixed contact. The load control device comprises a first loadterminal adapted to be coupled to either the power source or the load towhich the SPDT three-way switch is not coupled to, a second loadterminal coupled to the first fixed contact of the SPDT three-wayswitch, and a third load terminal coupled to the second fixed contact ofthe SPDT three-way switch. The load control device also comprises firstand second controllably conductive devices, each having conductive andnon-conductive states. The first and second controllably conductivedevices have respective first and second control inputs and are operableto enter the conductive state in response to first and second gatecurrents conducted through the first and second control inputs,respectively. The load control device further comprises a controlleroperable to control the first and second controllably conductivedevices. When the SPDT three-way switch is in the first state, thecontroller is operable to control the first controllably conductivedevice such that a load current is operable to flow through the secondload terminal when the first controllably conductive device is in theconductive state. When the SPDT three-way switch is in the second state,the controller is operable to control the first controllably conductivedevice such that the load current is operable to flow through the thirdload terminal when the controllably conductive device is in theconductive state. The controller is operable to determine, in responseto the magnitude of the first gate current through the first controlinput of the first controllably conductive device, whether the firstcontrollably conductive device is presently conducting current to theload, and to determine, in response to the magnitude of the second gatecurrent through the second control input of the second controllablyconductive device, whether the second controllably conductive device ispresently conducting current to the load.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form, which is presently preferred, it being understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown. The features and advantages of the presentinvention will become apparent from the following description of theinvention that refers to the accompanying drawings, in which:

FIG. 1A shows a prior art three-way switch system, which includes twothree-way switches;

FIG. 1B shows an example of a prior art three-way dimmer switch systemincluding one prior art three-way dimmer switch and one three-wayswitch;

FIG. 1C shows a prior art four-way switching system;

FIG. 1D shows a prior art extended four-way switching system;

FIG. 2 is a simplified block diagram of a typical prior art multiplelocation lighting control system;

FIG. 3 shows the prior art user interface of the dimmer switch of themultiple location lighting control system of FIG. 2;

FIG. 4 is a simplified block diagram of the dimmer switch and the remoteswitch of the prior art multiple location lighting control system ofFIG. 2;

FIG. 5A is a simplified block diagram of a three-way lighting controlsystem including a smart three-way dimmer according to the presentinvention;

FIG. 5B shows a state diagram summarizing the operation of the lightingcontrol system of FIG. 5A;

FIG. 5C is a perspective view of a user interface of the smart three-waydimmer of FIG. 5A;

FIG. 6A is a simplified block diagram of a three-way lighting controlsystem including a second embodiment of a smart three-way dimmeraccording to the present invention;

FIG. 6B is a simplified schematic diagram of a first detect circuit ofthe dimmer of FIG. 6A;

FIG. 7A is a simplified block diagram of a three-way lighting controlsystem including a third embodiment of a smart three-way dimmeraccording to the present invention;

FIG. 7B shows a simplified schematic diagram of a current detect circuitof the dimmer of FIG. 7A;

FIG. 8 is a simplified block diagram of a four-way lighting controlsystem including a smart four-way dimmer according to a fourthembodiment of the present invention;

FIG. 9 shows a state diagram summarizing the operation of the lightingcontrol system of FIG. 8;

FIG. 10 is a flowchart of a control loop of the controller of the smartfour-way dimmer of FIG. 8 for determining the state of the dimmer;

FIG. 11 is a flowchart of the process of the button routine of thecontrol loop of FIG. 10;

FIG. 12 is a flowchart of the process of the current detect routine ofthe control loop of FIG. 10;

FIG. 13 is a flowchart of the process of the triac state routine of thecontrol loop of FIG. 10;

FIG. 14 is a flowchart of the startup process of the controller of thedimmer switch of FIG. 8;

FIG. 15A is a simplified block diagram of a three-way system thatincludes a smart switch according to a fifth embodiment of the presentinvention;

FIGS. 15B and 15C are simplified diagrams showing waveforms of theoperation of the smart switch of FIG. 15A;

FIG. 15D is a simplified flowchart of a smart switch procedure executedby a controller of the smart switch of FIG. 15A;

FIG. 16A is a simplified block diagram of a three-way system thatincludes a smart switch according to a sixth embodiment of the presentinvention with the smart switch coupled to the line-side of the system;

FIG. 16B is a simplified schematic diagram showing current sensecircuits and a line voltage detect circuit of the smart switch of FIG.16A in greater detail;

FIG. 16C is a simplified block diagram of the three-way system of FIG.16A with the smart switch coupled to the load-side of the system;

FIGS. 17A and 17B are simplified diagrams showing waveforms of theoperation of the smart switch of FIG. 16A;

FIG. 18A is a simplified flowchart of a button procedure executed by acontroller of the smart switch of FIG. 16A;

FIGS. 18B and 18C are simplified flowcharts of a zero-crossing procedureexecuted by the controller of the smart switch of FIG. 16A;

FIG. 18D is a simplified flowchart of an ON routine executed by thecontroller of the smart switch of FIG. 16A;

FIG. 18E is a simplified flowchart of an OFF routine executed by thecontroller of the smart switch of FIG. 16A;

FIG. 19 is a simplified block diagram of a three-way system 1900 thatincludes a smart dimmer according to a seventh embodiment of the presentinvention;

FIGS. 20A and 20B are simplified diagrams showing waveforms of theoperation of the smart dimmer of FIG. 19; and

FIG. 21 is a simplified flowchart of a zero-crossing procedure executedby a controller of the smart dimmer of FIG. 19.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 5A is a simplified block diagram of a three-way lighting controlsystem 500 including a smart three-way dimmer switch 502 according tothe present invention. The dimmer 502 and a standard three-way switch504 are connected in series between an AC voltage source 506 and alighting load 508. The dimmer 502 includes a hot terminal H that iscoupled to the AC voltage source 506 and two dimmed hot terminals DH1,DH2 that are connected to the two fixed contacts of the three-way switch504. The common terminal of the three-way switch 504 is coupled to thelighting load 508. Alternatively, the dimmer 502 could be connected onthe load-side of the system 500 with the three-way switch 504 on theline-side. The dimmer 502 can be installed to replace an existingthree-way switch without the need to replace the other existingthree-way switch 504, and without the need for a wiring change to thethree-way switch being replaced. The terminals H, DH1, DH2 of the dimmer502 may be screw terminals, insulated wires or “flying leads”, stab-interminals, or other suitable means of connecting the dimmer to the ACvoltage source 506 and the lighting load 508.

In this embodiment of the smart two-wire dimmer switch 502, twobidirectional semiconductor switches 510, 514 are used. Thesemiconductor switches 510, 512 may comprise thyristors, such as triacsor silicon-controlled rectifiers (SCRs). Further, each semiconductorswitch 510, 512 may comprise another type of semiconductor switchingcircuit, such as, for example, a FET in a full-wave rectifier bridge,two FETs in anti-series connection, or one or more insulated-gatebipolar junction transistors (IGBTs). As shown in FIG. 5A, eachsemiconductor switch 510, 512 is implemented as a triac. The first triac510 has two main load terminals connected in series between the hotterminal H and the first dimmed hot terminal DH1. The first triac 510has a gate (or control input) that is coupled to a first gate drivecircuit 512. The second triac 514 has two main load terminals connectedin series between the hot terminal H and the second dimmed hot terminalDH2 and has a gate that is coupled to a second gate drive circuit 516.The first and second triacs 510, 514 are rendered conductive in responseto the conduction of gate currents through the respective gates of thetriacs.

The dimmer 502 further includes a controller 518 that is coupled to thegate drive circuits 512, 516 to control the conduction times of thetriacs 510, 514 each half-cycle. The controller 518 is preferablyimplemented as a microcontroller, but may be any suitable processingdevice, such as a programmable logic device (PLD), a microprocessor, oran application specific integrated circuit (ASIC). The controller 518drives the triacs 510, 514 to render the triacs conductive for a portionof each half cycle of the AC voltage source 506. Accordingly, thecontroller 518 is operable as to control the intensity of the lightingload 508 using a standard forward phase-control technique, as iswell-known to one of ordinary skill in the art.

As defined herein, “driving” refers to applying a control signal to agate of a thyristor (such as a triac or an SCR) to enable a gate currentto flow in the gate of the thyristor, such that the thyristor isconductive. When the thyristor is “conductive”, the gate current flowsthrough the gate of the thyristor and the thyristor is operable toconduct a load current. The load current is defined as a current havinga magnitude greater than the latching current of the thyristor. If thecurrent through the main load terminals of the thyristor exceeds thelatching current of the thyristor (while the thyristor is being driven),the thyristor then conducts the load current and the thyristor isdefined to be in “conduction”.

A power supply 520 generates a DC voltage, V_(CC), to power thecontroller 518. The power supply 520 is coupled from the hot terminal Hto the first dimmed hot terminal DH1 through a first diode 522 and tothe second dimmed hot terminal DH2 through a second diode 524. Thisallows the power supply 520 to draw current through the first dimmed hotterminal DH1 when the three-way switch 504 is in position A and throughthe second dimmed hot terminal DH2 when the three-way switch 504 is inposition B. The power supply 520 is able to charge when the triacs 510,514 are both not conducting and there is a voltage potential developedacross the dimmer 520.

The dimmer 502 further includes a zero-crossing detector 526 that isalso coupled between the hot terminal H and the dimmed hot terminalsDH1, DH2 through the diodes 522, 524, respectively. The zero-crossingdetector 526 provides a control signal to the controller 518 thatidentifies the zero-crossings of the AC supply voltage. The controller518 determines when to turn on the triacs 510, 514 each half-cycle bytiming from each zero-crossing of the AC supply voltage.

A user interface 528 is coupled to the controller 518 and to allow auser to determine a desired lighting level (or state) of the lightingload 508. The user interface 528 provides a plurality of actuators forreceiving inputs from a user. For example, the user interface 528 maycomprise a toggle button 560 (i.e., a tap switch) and an intensityactuator 570 (i.e., a slider control) as shown in FIG. 5C. In responseto an actuation of the toggle button 560, the controller 518 will togglethe state of the lighting load 508 (i.e., from on to off and vice versa)by changing which one of the two triacs 510, 514 is conducting. Thecontroller 518 drives the triacs 510, 514 conduct on a complementarybasis, such that only one of the two triacs operable to conduct the loadcurrent to the lighting load 508 at a single time. In this way, thedimmer 502 operates similarly to a standard SPDT switch by allowingcurrent to either flow through the first dimmed hot terminal DH1 or thesecond dimmed hot terminal DH2 solely in response to an actuation of thetoggle button 560. Alternatively, the user interface 528 may include aseparate on button and off button, which will cause the lighting load508 to turn on and off, respectively. Movement of the intensity actuator570 will cause the dimmer 502 to control the intensity of the lightingload 508.

Further, the user interface 528 may comprise a visual display forproviding feedback of the state of the lighting load 508 or the dimmer502 to the user. The visual display may comprise, for example, aplurality of light-emitting diodes (LEDs), which may be selectivelyilluminated by the controller 518. A visual display is described ingreater detail in previously-referenced U.S. Pat. No. 5,248,919.

The dimmer 502 further includes an airgap switch 530 for preventingcurrent flowing through either of the triacs 510, 514, and an inductor531 for providing electromagnetic interference (EMI) filtering.

When the three-way switch 504 is in position A and the desired state ofthe lighting load 508 is on, the controller 518 will turn the firsttriac 510 on for a portion of each half-cycle, while maintaining thesecond triac 514 in the non-conducting state. If the three-way switch504 is then toggled from position A to position B, current will not flowto the lighting load 508 since the second triac 514 is not conducting.Therefore, the lighting load 508 will not be illuminated. Alternatively,if the three-way switch 504 is in position A, the lighting load 508 ison, and the toggle button 560 of the user interface 528 is actuated, thecontroller 518 will cause the first triac 510 to stop conducting and thesecond triac 514 to begin conducting. The lighting load 508 will be offbecause the controller 518 is driving the second triac 514 while thethree-way switch 504 is in position A. If the toggle button 560 of theuser interface 528 is actuated again, the controller 518 will stopdriving the second triac 514 and will cause the first triac 510 to beginconducting, thus causing the lighting load 508 to illuminate again.

Similarly, when the three-way switch 504 is in position B and thedesired state of the lighting load 508 is on, the controller 518 willturn the second triac 514 on for a portion of each half-cycle, whilemaintaining the first triac 510 in the non-conducting state. If thethree-way switch 504 is then switched to position A, the current path tothe lighting load 508 is interrupted and the lighting load will be off.Also, if the three-way switch 504 is in position B, the lighting load508 is on, and the toggle button 560 of the user interface 528 isactuated, the controller 528 will cause the second triac 514 to stopconducting and the first triac 510 to begin conducting. The lightingload 508 will be off because the first triac 510 is conducting and thethree-way switch 504 is in position B.

The power supply 520 preferably has a large enough storage capacitor topower the controller 518 during the times when the three-way switch 504is transitioning from position A to position B and vice versa. Forexample, as the three-way switch 504 is toggled, current temporarilywill not flow through either of the dimmed hot terminals DH1, DH2 as themovable contact transitions and the power supply 520 will provide powerto the controller 518 by virtue of the internal storage capacitor. Theamount of power that the power supply 520 needs to provide when thethree-way switch 504 is transitioning is dependent on the transitioningtime required for the movable contact to move from one fixed contact tothe other.

However, it is not always possible to guarantee that the power supply520 will be able to power the controller 518 and other low voltagecircuitry during the time when the three-way switch 504 is transitioningbetween positions. Because of space limitations in a wall-mountabledimmer switch, it is not possible to simply include a particularly largestorage capacitor in the power supply 520 to provide power during thetransitioning time. Also, since the transitioning time is dependent onthe force that a user exerts on the actuator of the three-way switch504, the transitioning time can vary widely from one transition to thenext. All three-way switches 504 include a region of “dead travel”,i.e., when the movable contact of the three-way switch is approximatelyhalf way between position A and position B and is not contacting eitherof the fixed contacts. Sometimes, it is possible for the three-wayswitch 504 to be sustained in the region of dead travel, such that nocurrent may flow through the power supply 520 for an indeterminateperiod of time.

Accordingly, the dimmer 502 includes a memory 532 that enables thedimmer 502 to return to the appropriate state, i.e., to control thecorrect one of the two triacs 510, 514, if power to the dimmer 502 istemporarily lost when the three-way switch 504 is transitioning. Thememory 532 is coupled to the controller 518. Whenever the toggle button560 of the user interface 528 is actuated, the controller 518 stores inthe memory 532, which one of the triacs 510, 514 is presently beingcontrolled. In this way, if dimmer 502 temporarily loses power and theDC voltage V_(CC) falls below a level that allows for proper operationof the controller 518, the controller will read from the memory 532which triac 510, 514 to control at “power up”, i.e. when the DC voltageV_(CC) rises back above the level that ensures proper operation of thecontroller.

FIG. 5B shows a state diagram 550 summarizing the operation of thelighting control system 500 of FIG. 5A. Two states 552, 554 are shown inwhich the lighting load 508 will be on since the three-way switch 504 isin the correct position to complete the circuit through the conductingtriac. For example, at state 552, when the three-way switch 504 is inposition A, the first triac 510 is able to conduct current to thuscontrol the lighting load 508. The state diagram 550 also includes twostates 556, 558 in which the lighting load 508 will be off since thethree-way switch 504 is not in a position to conduct current through thetriac that is enabled for conduction. A transition between states can becaused by one of three actions: a toggle of the three-way switch 504from position A to position B (designated by ‘B’ in FIG. 5B), a toggleof the three-way switch 504 from position B to position A (designated by‘A’), and an actuation of the toggle button 560 of the user interface528 (designated by ‘T’).

FIG. 6A shows a simplified block diagram of a three-way lighting controlsystem 600 including a second embodiment of a smart three-way dimmerswitch 602 according to the present invention. A first detect circuit(or sensing circuit) 636 is coupled across the first triac 510 and asecond detect circuit (or sensing circuit) 638 is coupled across thesecond triac 514. The detect circuits 636, 638 provide control signalsto the controller 618 representative of electrical characteristics ofthe first dimmed hot terminal DH1 and the second dimmed hot terminalDH2, respectively. Each of the electrical characteristics may be avoltage developed across one of the respective triacs. Alternatively,the detect circuits 636, 638 may be placed in series with the dimmed hotterminals DH1, DH2 and the electrical characteristics may be currentsthrough the dimmed hot terminals. In essence, the sensing of theelectrical characteristics provides a determination of whether a path ofcontinuity exists between hot and neutral of the AC voltage source 506through the lighting load 508, the three-way switch 504, and thethree-way dimmer switch 602, at either the first dimmed hot terminal DH1or the second dimmed hot terminal DH2.

The controller 618 uses this information to determine the position ofthe three-way switch 504 in the system 600. For example, when thethree-way switch 504 is in position A and the first triac 510 isnon-conductive, a voltage will develop across the first detect circuit636, which will output a signal indicating that the three-way switch 504is in position A. Similarly, when the three-way switch 504 is inposition B, the second detect circuit 638 will output a correspondingsignal to the controller 618. The controller 618 uses the information ofthe state of the three-way switch 504 to provide feedback to the uservia a plurality of LEDs on a user interface 628 and may provide feedbackinformation to other control devices via an optional communicationcircuit 634. For example, the user interface 628 may be the same as theuser interface shown in FIG. 3.

The communication circuit 634 may be coupled to a communications link,for example, a wired serial control link, a power-line carrier (PLC)communication link, or a wireless communication link, such as aninfrared (IR) or a radio frequency (RF) communication link. An exampleof an RF lighting control system is described in commonly assigned U.S.Pat. No. 5,905,442, issued May 18, 1999, entitled METHOD AND APPARATUSFOR CONTROLLING AND DETERMINING THE STATUS OF ELECTRICAL DEVICES FROMREMOTE LOCATIONS, the entire disclosure of which is hereby incorporatedby reference.

Instead of providing complementary control of the triacs 510, 514, thecontroller 618 could control the triacs to the same state at the sametime. For example, when the first triac 510 is conducting and the secondvoltage detect circuit 638 determines that the three-way switch 504 hasbeen toggled to position B, the controller could cause both triacs tostop conducting since the desired lighting level of the lighting load508 is off. When neither triac 510, 514 is conducting, substantially nopower, i.e., only an amount of power that will not illuminate thelighting load 508, is conducted to the lighting load.

Accordingly, the controller is operable to detect a change of theposition of the three-way switch 504 and can determine when to togglepower to the load based on the three-way switch position change and thepresent state of the dimmer. Thus, the embodiments shown in FIGS. 5A and6A are compatible with a mechanical three-way switch 504.

FIG. 6B is a simplified schematic diagram of a possible implementationof the first detect circuit 636. Since the voltage provided across thedetect circuit 636 is an AC line voltage, the detect circuit includes anoptocoupler 640. A resistor 642 is provided in series with thephotodiodes 640A, 640B of the optocoupler 640 to limit the currentthrough the photodiodes. The voltage at the collector of thephototransistor 640C of the optocoupler 640 is provided to thecontroller 618. A resistor 646 is provided in series with thephototransistor 640C to pull the voltage provided to the controller 618up to the DC voltage V_(CC) of the power supply 520 when thephototransistor is not conducting (i.e., when there is no voltage acrossthe detect circuit 636).

When a voltage is produced across the detect circuit 636, current flowsthrough the photodiode 640A in the positive half-cycles and thephotodiode 640B in the negative half-cycles. Hence, the phototransistor640C conducts and the voltage at the collector of the phototransistor ispulled down to a circuit common 648. The schematic diagram of the seconddetect circuit 638 is identical to the schematic diagram of the firstdetect circuit 636 shown in FIG. 6B, differing only in the fact that thesecond detect circuit 638 is connected between the hot terminal H andthe second dimmed hot terminal DH2. Alternatively, the first and seconddetect circuits 636, 638 could be implemented as a simple resistivecircuit (not shown), for example, a resistor divider, with thecontroller 518 operable to detect a voltage produced by the resistivecircuit.

FIG. 7A shows a simplified block diagram of a three-way lighting controlsystem 700 including a third embodiment of a smart three-way dimmerswitch 702 according to the present invention. In this embodiment, thedimmer switch 702 includes a single controllably conductive device, forexample, a bidirectional semiconductor switch, such as a triac 710. Acontroller 714 is coupled to the gate of the triac 710 through a gatedrive circuit 712 and controls the conduction time of the triac eachhalf-cycle. A power supply 716 is coupled across the triac 710 andgenerates a DC voltage VCC to power the controller 714. A zero-crossingdetector 718 determines the zero-crossing points of the AC voltagesource 506 and provides this information to the controller 714. A userinterface 720 provides inputs to the controller 714 from a plurality ofbuttons (including a toggle button) and includes a plurality of LEDs forfeedback to a user. A communication circuit 722 allows the controller714 to transmit and receive messages with other control devices. Anairgap switch 724 disconnects the dimmer switch 702 and the lightingload 508 from the AC voltage source 506. An inductor 725 is in serieswith the triac 710 and provides EMI filtering. A memory 726 stores thepresent state of the dimmer switch 702, such that the controller 714 canproperly operate the triac 710 at power up.

The dimmer 702 also includes a current detect circuit (sensing circuit)728 that is coupled between the first dimmed hot terminal DH1 and thesecond dimmed hot terminal DH2. The current detect circuit 728 isoperable to detect when there is current flowing through the seconddimmed hot terminal DH2 and to accordingly provide a control signal tothe controller 714. The power supply 716 provides a current path throughthe current detect circuit 728 when the triac 710 is non-conducting.When the three-way switch 504 is in position B, the charging currentthrough the power supply 716 will flow through the second dimmed hotterminal DH2. The current detect circuit 728 will sense the chargingcurrent and indicate to the controller 714 that the three-way switch isin position B. When the three-way switch 504 is in position A, nocurrent will flow through the current detect circuit 728 and no signalwill be provided to the controller 714. Thus, the controller 714 is ableto determine the state of the three-way switch 504 and to control thestate of the lighting load 508 (i.e., on or off) accordingly.

The memory 726 stores the state of the triac 710 and of the three-wayswitch 504. If the power supply 716 is unable to supply power to thecontroller 714 through the duration of a transition of the three-wayswitch 504, the controller 714 will reset, i.e., power down and thenpower up when the three-way switch 504 has finished the transition. Atpower up, the controller 714 of the dimmer 702 checks the status of thethree-way switch 504 from the control signal of the current detectcircuit 728 and compares the present state of the three-way switch tothe state of the three-way switch that is stored in the memory 726. Ifthe status of the three-way switch 504 has changed, the controller 714will toggle the state of the triac 710 based on the present state of thetriac that is stored in the memory 726.

FIG. 7B shows a simplified schematic diagram of the current detectcircuit (sensing circuit) 728 of the dimmer 702. The current detectcircuit 728 includes a current sense transformer 730 that has a primarywinding coupled in series between the dimmed hot terminals DH1, DH2. Thecurrent sense transformer 730 only operates above a minimum operatingfrequency, for example, 100 kHz, such that current only flows in thesecondary winding when the current waveform through the primary windinghas a frequency above the minimum operating frequency. The current sensetransformer 730 detects the falling edge of the current waveform throughthe power supply 716 when the charging current flows through the seconddimmed hot terminal DH2. Since the dimmer 702 is using a triac as thesemiconductor switch, the dimmer operates using forward phase controldimming, in which the triac 710 is non-conductive at the beginning ofeach half-cycle. Thus, the power supply 716 charges at the beginning ofeach half-cycle. When the power supply 716 stops charging during ahalf-cycle, the charging current through the power supply will drop tozero. Since the falling time of the current waveform through the primarywinding of the current sense transformer 730 is very short (i.e., thewaveform has a high-frequency component), a current will flow in thesecondary of the current sense transformer when the switch 504 is inposition B. An example of the current sense transformer 730 is partnumber CT319-200, manufactured by Datatronic, Ltd.

The secondary winding of the current sense transformer 730 is coupledacross a resistor 732. The resistor 732 is further coupled betweencircuit common and the negative input of a comparator 734. A referencevoltage is produced by a voltage divider comprising two resistors 736,738 and is provided to the positive input of the comparator 734. Theoutput of the comparator 734 is tied to V_(CC) through a resistor 740and is coupled to the controller 714. When current flows through thesecondary winding of the current sense transformer 730, a voltage isproduced across the resistor 732 that exceeds the reference voltage. Thecomparator 734 then drives the output low, signaling to the controller714 that current has been sensed. Alternatively, the current detectcircuit 728 may be implemented using an operational amplifier or adiscrete circuit comprising one or more transistors rather than thecomparator 734.

FIG. 8 is a simplified block diagram of a four-way lighting controlsystem 800 including a smart four-way dimmer switch 802 according to afourth embodiment of the present invention. The dimmer 802 and twothree-way switches 803, 804 are coupled between an AC voltage source 806and a lighting load 808. The dimmer 802 has replaced the four-way switch185 in the four-way lighting control system 180 of FIG. 1C.

The dimmer 802 operates on the same principles as the dimmer 702 of FIG.7A. However, the dimmer 802 includes an additional hot terminal H2 thatis coupled to the three-way switch 803 on the line-side of the system802. The dimmer 802 further comprises a second current detect circuit(sensing circuit) 829 that is coupled between the hot terminals H, H2and provides a signal to a controller 814. The second current detectcircuit 829 operates in the same manner as the first current detectcircuit 728. When current is detected flowing through the second currentdetect circuit 829, the controller 814 determines that the line-sidethree-way switch 803 is in position D. When no current is flowingthrough the second current detect circuit 829, the three-way switch 803is in position C. Thus, the controller 814 is able to determine thestates of both the line-side three-way switch 803 and the load-sidethree-way switch 804 and to operate the triac 710 accordingly. Wheneither three-way switch 803, 804 is toggled, or the toggle button of theuser interface 720 is actuated, the controller 714 will toggle the stateof the lighting load 808.

Even though the four-way dimmer switch 802 has four connections, thedimmer could be installed in a three-way system (in place of thethree-way dimmer switch 502 in FIG. 5A or three-way dimmer switch 702 inFIG. 7A). One of the additional terminals DH2 or H2 would not beconnected in the system 800. So, the dimmer 802 allows for a singledevice that can be installed in any location of a four-way or three-waysystem without the need to determine in advance what kind of switch thedimmer will be replacing.

FIG. 9 shows a state diagram 900 summarizing the operation of thelighting control system 800 of FIG. 8. In four states 902, 904, 906,908, the triac 710 will be conducting since the desired state of thelighting load 808 is on. The state diagram 900 also shows four states912, 914, 916, 918 in which the desired state of the lighting load 808is off. A transition between states can be caused by one of fiveactions: a toggle of the three-way switch 804 from position A toposition B (designated by ‘B’ in FIG. 6B), a toggle of the three-wayswitch 804 from position B to position A (designated by ‘A’), a toggleof the three-way switch 803 from position C to position D (designated by‘D’), a toggle of the three-way switch 803 from position D to position C(designated by ‘C’), and an actuation of the toggle button of the userinterface 720 (designated by ‘T’) (or when a “toggle” signal is receivedvia the communication circuit 722). Note that in all states of the statediagram 900, the triac 710 is operable to conduct current to thelighting load 808 to control the state of the lighting load independentof the states of the three-way switches 803, 804.

The state diagram 900 thus identifies the status of the three-way switch803, the three-way switch 804, and the triac 710 (and thus the lightingload 808) for all possible states and shows all the state transitionswhen the three-way switches 803, 804 are toggled and the toggle buttonof the user interface 720 is actuated (or when a “toggle” signal isreceived via the communication circuit 722).

FIG. 10 is a flowchart of a state control procedure 1000 of thecontroller 814 for determining the state of the dimmer 802. The statecontrol procedure 1000 runs periodically, for example, approximatelyevery 6 msec. The state control procedure 1000 includes a button routine1100, a current detect routine 1200, and a triac state routine 1300.While the button routine 1100, the current detect routine 1200, and thetriac state routine 1300 are shown executing in sequential order in FIG.10, these routines alternatively could each be called from differentpieces of software and each be executed at a different interval.

The controller 814 utilizes a FIFO (first in, first out) stack to storerequests for the triac state routine 1300 to change the state of thetriac 710. The button routine 1100 and the current detect routine 1200are both operable to load an event (for example, a “toggle event”) intothe FIFO stack. The triac state routine loads these events from the FIFOstack and processes the events. In the discussion of FIGS. 10 through14, only toggle events are discussed. However, other events, such as“increase intensity” or “decrease intensity”, could be loaded into theFIFO stack by other routines (not described).

In the state control procedure 1000, the controller 814 utilizes threevariables: TRIAC_STATUS, 1ST_DETECT, and 2ND_DETECT that are stored inthe memory 726. The variable TRIAC_STATUS stores the conduction state ofthe triac 710, i.e., either ON or OFF. The variables 1ST_DETECT and2ND_DETECT store the state of the first current detect circuit 728 andthe second current detect circuit 829, respectively. The possible valuesfor the variables 1ST_DETECT and 2ND_DETECT are TRUE (when current isdetected) and FALSE (when current is not detected).

A flowchart describing the process of the button routine 1100 is shownin FIG. 11. At step 1110, the controller 814 first checks the togglebutton of the user interface 720. If the toggle button is being pressedat step 1112, the controller 814 will load a “toggle event” into theFIFO stack at step 1114 and exit the process. If the toggle button isnot being pressed at step 1112, the process simply exits.

FIG. 12 is a flowchart of the process of the current detect routine1200. The outputs of the first current detect circuit 728 and secondcurrent detect circuit 829 are coupled to separate interrupt inputs onthe controller 814. Whenever an input is provided from the first currentdetect circuit 728, a first interrupt routine is executed to set a firstcurrent detect flag. Similarly, whenever an input is provided from thefirst current detect circuit 728, a second interrupt routine is executedto set a second current detect flag.

Referring to FIG. 12, the first current detect flag is first checked atstep 1210. At step 1212, if the first current detect flag has changedstates, i.e., the new state of the first current detect circuit is notequal to the value stored in the variable 1ST_DETECT, the process movesto step 1214, where a determination is made as to whether the presentvalue of the variable 1ST_DETECT is equal to TRUE. If so, the variable1ST_DETECT is set to FALSE at step 1216. Otherwise, the variable1ST_DETECT is set to TRUE at step 1218. Next, the controller 814 willload a “toggle event” into the FIFO stack at step 1220.

After loading a toggle event into the FIFO stack at step 1220, or afterdetecting no change of state of the first current detect circuit 728 atstep 1212, the output of the second current detect circuit 829 ischecked at step 1222. At step 1224, if the output of the second currentdetect circuit 829 has changed states, i.e., the new state of the secondcurrent detect circuit is not equal to the value stored in the variable2ND_DETECT, a determination is made as to whether the present value ofthe variable 2ND_DETECT is equal to TRUE at step 1226. If so, thevariable 2ND_DETECT is set to FALSE at step 1228; otherwise, thevariable 2ND_DETECT is set to TRUE at step 1230. Next, the controller714 will load a toggle event into the FIFO stack at step 1232 and exit.

At step 1224, if the output of the second current detect circuit 829 hasnot changed states, then the process simply exits without loading atoggle event into the FIFO stack.

FIG. 13 is a flowchart of the process of the triac state routine 1300.First, a toggle event is loaded from the FIFO stack (and deleted fromthe stack at the same time) at step 1310. If there is a toggle event inthe FIFO stack to handle at step 1312, the triac state will be toggled.At step 1314, if the variable TRIAC_STATE is equal to OFF, then thevariable TRIAC_STATE is set to ON at step 1316. Otherwise, the variableTRIAC_STATE is set to OFF at step 1318. At step 1320, the variablesTRIAC_STATE, 1ST_DETECT, and 2ND_DETECT are stored in the memory 726.The process loops until there are no toggle events to handle at step1312, at which time the process exits.

FIG. 14 is a flowchart of the startup process 1400 that the controller814 performs at power up, for example, if the controller 814 loses powerwhile a connected three-way or four-way switch is transitioning. First,the controller 814 reads the variables TRIAC_STATE, 1ST_DETECT, and2ND_DETECT from the memory 726 at step 1410. Next, the controller 814checks the status of the first current detect circuit 728 and the secondcurrent detect circuit 829 in the current detect routine 1100. Next, thecontroller 814 determines whether to change the variable TRIAC_STATE inthe triac state routine 1200. Finally, the process exits to begin normaloperation executing the state control procedure 1000 of FIG. 10.

Although the embodiment of FIG. 8 shows two current detect circuits 728,829. Additional sensing circuits could be employed. For example, acurrent detect circuit could be employed coupled in series with eachterminal of the smart four-way dimmer switch 802 for a total of fourcurrent detect circuits.

The smart dimmers 502, 602, 702, and 802 preferably control incandescentand magnetic-low voltage loads using standard forward phase-controltechniques. With such load types, the power supplies of the dimmers areable to draw a small amount of current through the loads withoutilluminating the loads. However, other load types, such as fluorescentloads, are susceptible to illuminating when even a small amount ofcurrent flows though the load. Since the dimmer topologies of FIG.5A-FIG. 8 depend upon current flowing through the load in order todetermine the state of a connected three-way or four-way switch, it isnot preferable to use the smart dimmers 502, 602, 702, and 802 tocontrol those load types that may illuminate due to a low amount ofcurrent flowing through the load. It is therefore desirable to providean electronic three-way load control device, such as an electronicswitch, which is able to control a wide variety of load types.

FIG. 15A is a simplified block diagram of a three-way system 1500 thatincludes a smart electronic switch 1502 according to a fifth embodimentof the present invention. The smart switch 1502 and a three-way switch1504 are coupled between an AC voltage source 1506 and a lighting load1508. The smart switch 1502 includes two semiconductor switches, e.g.,two triacs 1510, 1514, coupled between the hot terminal and respectiveswitched hot terminals SH1, SH2. A controller 1518 controls the triacs1510, 1514 (via two gate drive circuits 1512, 1516) on a complementarybasis, i.e., in a similar manner as the smart dimmer 502 of FIG. 5A.Accordingly, when the first triac 1510 is conductive, the second triac1514 is non-conductive, and when the second triac 1514 is conductive,the first triac 1510 is non-conductive. The switch 1502 further includesan airgap switch 1530 for preventing current flowing through either ofthe triacs 1510, 1514, and an inductor 1531 for providingelectromagnetic interference (EMI) filtering.

The smart switch 1502 includes a power supply 1520 that is coupledbetween the hot terminal H and a neutral terminal N, such that nocurrent is drawn through the lighting load 1508 in order to charge thepower supply 1520. The power supply 1520 generates a DC voltage forpowering a controller 1518. The DC voltage V_(CC) is referenced tocircuit common, i.e., the neutral terminal N. A user interface 1528includes a toggle button for toggling the lighting load 1508 between onand off, and an LED for displaying the state of the lighting load.

The smart switch 1502 further comprises two sense circuits 1536, 1538,and a resistor 1560 coupled between the first and second switched hotterminals SH1, SH2. The sense circuits 1536, 1538 operate aszero-crossing detectors (to allow the controller 1518 to phase controlthe triacs 1510, 1512 appropriately) and as voltage detect circuits (toallow the controller to determine the state of the connected three-wayswitch 1504 and thus the state of the lighting load 1508. In response todetermining the state of the three-way switch 1504, the controller 1508may illuminate the LED of the user interface 1528, or transmit feedbackinformation to other control devices via a communication circuit 1534.The controller 1518 is coupled to a memory 1532 for storage of the stateof the triacs 1510, 1512 and the three-way switch 1504.

The first sense circuit 1536 comprises a resistor divider, whichincludes two resistors 1540, 1542 and is coupled between the switchedhot terminal SH1 and circuit common, i.e., the neutral terminal N. Thejunction of the resistors 1540, 1542 is coupled to the base of an NPNbipolar junction transistor (BJT) 1544. The collector of the transistor1544 is coupled to the DC voltage Vcc through a resistor 1546 (e.g.,having a resistance of 15 kΩ) and is provided as an output to thecontroller 1518. The resistors 1540, 1542 preferably have resistances of110 kΩ and 4.7 kΩ, respectively, such that when the switched hot voltageat the switched hot terminal SH1 is below a predetermined level, e.g.,approximately 17 V, the output to the controller 1518 is pulled up toapproximately the DC voltage Vcc. When the dimmed hot voltage exceedsthe predetermined level, the transistor 1544 begins to conduct, pullingthe output to approximately circuit common.

The second sense circuit 1538 includes similar components as the firstsense circuit 1536 and operates in the same manner. The second sensecircuit 1538 comprises resistors 1550, 1552, 1556 and an NPN bipolarjunction transistor 1554. Since the controller 1518 drives the triacs1510, 1514 on a complementary basis and the sense circuits 1536, 1538are referenced to the neutral terminal N, the controller 1518 isoperable to receive the zero-crossing information of the AC power supply1506 independent of the position of the three-way switch 1504.

The controller 1518 also uses the sense circuits 1536, 1538 to determinethe state of the connected three-way switch 1504. When the controller1518 is driving the second triac 1514, the second sense circuit 1538 isoperatively coupled between the hot terminal H and the neutral terminalN at the beginning of each half cycle of the AC voltage source 1506. Asshown in FIG. 15B, a second switched hot voltage V_(TRAVELER 2) isprovided at the second switched hot terminal SH and a secondzero-crossing signal V_(ZC2) is generated at the output of the secondsense circuit 1538. The first sense circuit 1536 is coupled to thesecond switched hot terminal SH1 through the resistor 1560.

When the three-way switch 1504 is in position B, a first switched hotvoltage V_(TRAVELER 1) is provided at the first switched hot terminalSH1 and is a scaled version of the second switched hot voltageV_(TRAVELER 2). A first zero-crossing signal V_(ZC1), having differentshape than the second zero-crossing signal V_(ZC2), is generated at theoutput of the first sense circuit 1536 as shown in FIG. 15B. However,when the three-way switch 1504 is in position A, the first switch hotvoltage V_(TRAVELER 1) has a magnitude of substantially zero volts (asshown in FIG. 15C) since the impedance of the lighting load 1508 (e.g.,approximately 400Ω or less) is much smaller than the impedance of thefirst sense circuit 1536 (i.e., the sum of the resistances of theresistors 1540, 1542). As a result, the first zero-crossing signalV_(ZC1) also has a magnitude of substantially zero volts.

When the controller 1518 is driving the second triac 1514, thecontroller is operable to determine the state of the connected three-wayswitch 1504 in response to whether the first zero-crossing signalV_(ZC1) is being provided or not. Similarly, when the controller 1518 isdriving the first triac 1510, the controller is operable to determinethe state of the connected three-way switch 1504 in response to whetherthe second zero-crossing signal V_(ZCs) is being provided or not. Insummary, the controller 1518 is operable to determine that the lightingload 1508 is on if both zero-crossing signals V_(ZC1), V_(ZC2) are beinggenerated and to determine that the lighting load 1508 is off if onlyone of the two zero-crossing signals V_(ZC1), V_(ZC2) is beinggenerated.

FIG. 15D is a simplified flowchart of a smart switch procedure 1570,which is executed by the controller 1518 periodically, e.g., once everyhalf-cycle of the AC voltage source 1506. First, the controller 1518checks to determine if the toggle button of the user interface 1528 isbeing pressed at step 1572. If the toggle button is being pressed atstep 1574, the controller 1518 changes which triac 1510, 1514 is beingdriven in a complementary manner. In other words, if the controller 1518is presently driving the first triac 1510 at step 1576, the controllerbegins to drive the second triac 1514 at step 1578. If the controller1518 is not presently driving the first triac 1510 at step 1576, thecontroller begins to drive the first triac at step 1580.

Next, the controller 1518 checks the inputs from the first and secondsense circuits 1536, 1538 (i.e., the first and second zero-crossingsignals V_(ZC1), V_(ZC2)) at step 1582 in order to determine the stateof the connected three-way switch 1504 and the state of the lightingload 1508. If the controller 1518 is receiving both of the zero-crossingsignals V_(ZC1), V_(ZC2) at step 1584, the controller 1518 determinesthat the lighting load 1508 is on at step 1586 an the procedure 1570exits. The controller 1518 is operable to then illuminate the LED of theuser interface 1528 or to transmit feedback information via thecommunication circuit 1534. If controller 1518 is not receiving both ofthe zero-crossing signals V_(ZC1), V_(ZC2) at step 1584, but thecontroller is receiving only one of the two zero-crossing signalsV_(ZC1), V_(ZC2) at step 1588, the controller determines that thelighting load 1508 is off at step 1590 and the procedure 1570 exits.

FIG. 16A is a simplified block diagram of a three-way system 1600 thatincludes a smart switch 1602 according to a sixth embodiment of thepresent invention. As with the smart switch 1502 of FIG. 15A, the smartswitch 1602 includes two triacs 1510, 1514, which are controlled by acontroller 1618 in a complementary manner. A first zero-crossingdetector 1626 is coupled between the first switched hot terminal SH1 andthe neutral terminal N, and a second zero-crossing detector 1627 iscoupled between the second switched hot terminal SH2 and the neutralterminal N. The controller 1618 receives the zero-crossing signalsrepresentative of the zero-crossings of the AC voltage source 1506 fromthe first and second zero-crossing detectors 1626, 1627. The first andsecond zero-crossing detectors 1626, 1627 have similar structures as thefirst and second sense circuits 1526, 1528 of the smart dimmer 1502 ofFIG. 15A.

The smart switch 1602 further comprises first and second gate drivecircuits 1612, 1616 coupled in series between the gate and one of themain load terminals of each of the first and second triacs 1510, 1514,respectively. The first gate drive circuit 1612 includes a triggercircuit 1640, which is responsive to the controller 1618, and a currentsense circuit 1642, which provides an active-low gate current (GC)control signal to the controller. The controller 1618 is operable todrive the first triac 1510 by controlling the trigger circuit 1640 toconduct the gate current through the gate of the first triac 1510 tothus render the first triac conductive at a predetermined time eachhalf-cycle of the AC voltage source 1506. The GC control signal isgenerated by the current sense circuit 1642 and comprises a DC voltagerepresentative of the magnitude of the gate current. The controller 1618is operable to determine if the gate current is flowing through the gateof the first triac 1510 in response to the GC control signal. The gateof the first triac 1510 is coupled to the trigger circuit 1640 via aresistor 1646 and to the second of the main load terminals via aresistor 1648. The resistors 1646, 1648 preferably both have resistancesof 220Ω.

The second gate drive circuit 1616 has a similar structure as the firstgate drive circuit 1612 and comprises a trigger circuit 1650 and acurrent sense circuit 1652. The gate of the second triac 1514 is coupledto the trigger circuit 1650 via a resistor 1656 (e.g., 220Ω) and to thesecond of the main load terminals via a resistor 1658 (e.g., 220Ω).

The smart switch 1602 further comprises a line voltage detect (LVD)circuit 1660, which is coupled between the hot terminal H and theneutral terminal N. The line voltage detect circuit 1660 provides anactive-low LVD control signal to the controller 1618. The controller1618 is operable to determine whether the AC line voltage is present atthe hot terminal H in response to the line voltage detect circuit 1660.The line voltage detect circuit 1660 allows the controller 1618 todetermine if the lighting load 1508 is on when the dimmer 1602 iscoupled to the load side of the system 1600 (as shown in FIG. 16C).Accordingly, the controller 1618 is operable to determine the state ofthe three-way switch 1504 and the lighting load 1508 in response to thecurrent sense circuits 1642, 1652 and the line voltage detect circuit1660.

FIG. 16B is a simplified schematic diagram showing the current sensecircuits 1642, 1652 and the line voltage detect circuit 1660 in greaterdetail. The line voltage detect circuit 1660 preferably operates as azero-crossing detector and has a similar structure as the first andsecond sense circuits 1526, 1528 of the smart dimmer 1502 of FIG. 15A.The resistors 1662, 1664, 1668 have resistances of 110 kΩ, 1.0 kΩ, and15 kΩ, respectively. When the line voltage detect circuit 1660 does notprovide a zero-crossing signal to the controller 1618, the controller isoperable to determine that the lighting load 1508 is off.

The trigger circuit 1640 of the first gate drive circuit 1612 comprisesan opto-triac, having an input (i.e., a photo-diode) coupled between thecontroller 1618 and circuit common, and an output (i.e., a photo-triac)coupled in series with the gate of the first triac 1510. The currentsense circuit 1642 comprises an opto-coupler having an input (i.e., twophoto-diodes) coupled in series with the gate of the first triac 1510and the photo-triac of the opto-triac. The opto-coupler also includes anoutput (i.e., a photo-transistor), coupled between the controller 1618and circuit common. When the gate current is not flowing through eitherof the photo-diodes of the opto-coupler, the photo-transistor isnon-conductive and the output provided to the controller 1618 is pulledup to substantially the DC voltage Vcc through a resistor 1644. However,when the gate current is flowing, the photo-transistor pulls the outputto the controller 1618 to substantially circuit common (i.e.,approximately zero volts). The second gate drive circuit 1616 has asimilar structure as the first gate drive circuit 1612. The first andsecond gate drive circuits 1612, 1616 are characterized such that thecurrent sense circuits 1642, 1652 signal to the controller 1618 that thegate current is flowing (i.e., pull the GC control signal low) when thegate current has a magnitude of approximately 1 mA or greater.

FIG. 17A is a simplified diagram showing waveforms of the operation ofthe smart switch 1602 when the smart switch is coupled to the line sideof the system 1600 (as shown in FIG. 16A), the controller 1618 isdriving the first triac 1510, and the three-way switch 1504 is inposition A, such that the lighting load 1508 is on. Since the AC linevoltage signal is present at the hot terminal H, the line voltage detectcircuit 1660 drives the LVD control signal low around the peak of the ACline voltage signaling to the controller 1618 that the AC line voltageis present. The controller 1618 cannot determine the state of thelighting load 1508 from the LVD control signal, but must check one ofthe GC control signals.

The gate current for the first triac 1510 flows through the AC voltagesource 1506, the first triac 1510, the trigger circuit 1640, the currentsense circuit 1642, and the first zero-crossing detector 1626 to theneutral terminal N. Immediately after each zero-crossing of the AC linevoltage, the controller 1618 drives the trigger circuit 1640 to fire thefirst triac 1510. Accordingly, the gate current flows into the gate ofthe first triac for a period of time until the load current through themain terminals of the triac exceeds a latching current rating and thetriac becomes conductive. The voltage across the triac 1510 then dropsto a substantially low voltage (e.g., approximately 1 V) and the gatecurrent stops flowing. Therefore, the gate current exists as a pulse ofcurrent when the triac successfully fires. The GC control signalgenerated by the current sense circuit 1642 is low (i.e., atsubstantially zero volts) when the gate current is following, and ishigh (i.e., at substantially the DC voltage V_(CC)) when the gatecurrent is flowing as shown in FIG. 17A.

FIG. 17B is a simplified diagram showing waveforms of the operation ofthe smart switch 1602 when the smart switch is coupled to the line sideof the system 1600 and the controller 1618 is driving the first triac1510, but the three-way switch 1504 is in position B, such that thelighting load 1508 is off. In this case, the first triac 1510 does notbecome conductive since the current through the main terminals of thetriac cannot exceed the latching current rating. The impedance of thezero-crossing detector 1626 (e.g., approximately 60 kΩ) sets themagnitude of the gate current to a voltage below the latching currentrating of the first triac 1510. Since the first triac 1510 does notbecome conductive, the gate current continues to flow and has amagnitude greater than substantially zero amps (i.e., approximately 1 mAor greater as determined by the impedance of the zero-crossing detector1626) for substantially the length of each half-cycle. Accordingly, theGC control signal is pulled low to circuit common (i.e., toapproximately zero volts) for substantially the entire length of eachhalf-cycle, signaling that the first triac 1512 is not conducting theload current.

When the smart switch 1602 is coupled to the line-side of the system1600 (as shown in FIG. 16A), the controller 1618 is operable todetermine the state of the lighting load 1508 in response to the currentsense circuits 1642, 1652. Specifically, the controller 1618 monitorsthe output of the current sense circuit 1642, 1652 that is coupled inseries with the gate of the triac that is presently being driven duringa sampling window near the peak of the AC line voltage. If the gatecurrent is not flowing (i.e., the gate current has a magnitude ofsubstantially zero amps), the controller 1618 determines that the triacis conductive and the lighting load 1508 is on. If the gate current isflowing (i.e., the gate current has a magnitude greater thansubstantially zero amps), the controller 1618 determines that the triacis not conducting current to the load and the lighting load 1508 is off.

Preferably, the sampling window is a period of time having a lengthT_(WINDOW) (e.g., approximately 1.5 msec) centered around a timet_(PEAK) corresponding to the peak of the AC line voltage as shown inFIGS. 17A and 17B. The sampling window is centered around the peak ofthe AC line voltage to ensure that the controller 1618 does not samplethe GC control signal around the zero-crossings. Near thezero-crossings, the opto-triacs of the trigger circuits 1640, 1650 ofthe first and second gate drive circuits 1612, 1614 may not havesufficient current flowing through the photo-triacs to remainconductive. This may cause the opto-couplers of the current sensecircuits 1642, 1652 to allow the GC control signal to be high (i.e., thesame condition as when one of the triacs 1510, 1514 has becomeconductive and the gate current has stopped flowing).

When the smart switch 1602 is coupled to the load-side of the system1600 (as shown in FIG. 16C), the controller 1618 cannot determine thestate of the lighting load 1508 solely from the current sense circuits1642, 1652. The controller 1618 must also use the line voltage detectcircuit 1660 determine the state of the lighting load 1508. If thecontroller 1618 is not driving the triac 1510, 1514 that is in serieswith the present position of the three-way switch 1504, the AC linevoltage is not present across the line voltage detect circuit 1660. Theline voltage detect circuit 1660 provides an appropriate control signalto the controller 1618, which concludes that the lighting load 1508 isoff. If the AC line voltage is coupled across the line voltage detectcircuit 1660 and the gate current is flowing through the gate of thetriac that the controller 1618 is driving, the controller determinesthat the lighting load 1508 is on.

FIG. 18A is a simplified flowchart of a button procedure 1800 executedby the controller 1618 periodically, e.g., once every 10 msec, todetermine if the toggle button of the user interface 1528 is beingpressed. The controller 1618 uses a variable BUT_COUNT to keep track ofhow long the toggle button has been pressed. Specifically, the variableBUT_COUNT keeps track of how many consecutive times that the buttonprocedure 1800 is executed while the toggle button is pressed.

Referring to FIG. 18A, the controller 1618 first checks the inputprovided from the user interface 1528 at step 1810 to determine if thetoggle button of the user interface is being pressed. If the togglebutton is not being pressed at step 1812, the controller 1618 clears thevariable BUT_COUNT at step 1814. However, if the toggle button is beingpressed at step 1812, the controller increments the variable BUT_COUNTat step 1816. If the variable BUT_COUNT is not equal to a maximum value,e.g., two (2), at step 1818, the button procedure 1800 simply exits.

If the variable BUT_COUNT is equal to two at step 1818 (i.e., the togglebutton has been pressed during two consecutive executions of the buttonprocedure 1800), a determination is made at step 1820 as to whether thecontroller 1618 is presently controlling the first triac 1510. If so,the controller 1618 begins to control the second triac 1514 eachhalf-cycle at step 1822 (as will be described in greater detail below).If the controller 1618 is not controlling the first triac 1510 at step1820, the controller begins to control the second triac 1514 eachhalf-cycle at step 1824. Finally, the variable BUT_COUNT is cleared atstep 1826 and the button procedure 1800 exits.

FIGS. 18B and 18C are simplified flowcharts of a zero-crossing procedure1830 executed by the controller 1618 periodically in response toreceiving an indication of a zero-crossing from either one of thezero-crossing detectors 1626, 1627, i.e., once every half cycle of theAC voltage source 1506. After the zero-crossing at step 1832 eachhalf-cycle, the controller 1618 first renders one of the first andsecond triacs 1510, 1514 conductive substantially immediately followingthe zero-crossing (i.e., as soon as the magnitude of the AC line voltageis high enough that the triacs 1510, 1514 may be fired). Specifically,if the controller 1618 is controlling the first triac 1510 at step 1834,the controller drives the first triac via the first gate drive circuit1612 at step 1836. Alternatively, if the controller 1618 is controllingthe second triac 1514 at step 1834, the controller drives the secondtriac via the second gate drive circuit 1616 at step 1838. If thecontroller 1618 determines that the present half-cycle is the negativehalf-cycle at step 1840, the controller waits for the end of thehalf-cycle at step 1854, after which the controller stops driving theappropriate triac 1510, 1514 at step 1856.

If the present half-cycle is the positive half-cycle at step 1840, thecontroller 1618 determines at step 1842 whether the AC line voltage hasentered the sampling window, i.e., the period of time of 1.5 msecsurrounding the peak of the AC line voltage as shown in FIGS. 17A and17B. The controller 1618 waits at step 1842 until the AC line voltage isin the sampling window, at which time, the controller begins toperiodically sample the LVD control signal and the GC control signal todetermines if the AC line voltage is present at the hot terminal H andthe gate current is flowing through the gate of one of the first andsecond triacs 1510, 1514, respectively. Preferably, the controller 1618samples the control signals approximately every 250 μsec, such that thecontroller obtains approximately six (6) samples of each of the controlsignals during the sampling window. The controller 1618 uses twovariables LVD_COUNT and GC_COUNT to keep track of how many of the sixsamples of the LVD control signal is high and the GC_COUNT controlsignal is low during the sampling window, respectively.

Referring to FIG. 18C, the controller 1618 checks the LVD control signalfrom the line voltage detect circuit 1660 at step 1844 to determinewhether the AC line voltage is present at the hot terminal H. If the ACline voltage is not detected at step 1846, the controller 1618increments the variable LVD_COUNT at step 1848. If the variableLVD_COUNT is equal to a maximum value, e.g., two (2), at step 1850(i.e., two of the six samples of the LVD control signal are high duringthe sampling window), the controller 1618 executes an OFF routine 1890,which will be explained in greater detail below with reference to FIG.18E. The OFF routine 1890 provides some digital filtering to ensure thatthe state of the lighting load 1508 as determined by the controller 1618does not change too often. The zero-crossing procedure 1830 must executethe OFF routine 1890 during a predetermined number of consecutivehalf-cycles, e.g., approximately twelve (12) consecutive half-cycles,before the controller 1618 determines that the lighting load 1508 isoff. After executing the OFF routine 1890, the controller 1618 clearsthe variables LVD_COUNT and GC_COUNT at step 1852. At the end of thehalf-cycle at step 1854, the controller 1618 stops driving theappropriate triac 1510, 1514 at step 1856 and the procedure 1830 exits.

If the AC line voltage is detected at step 1846 or if the variableLVD_COUNT is not equal to two at step 1850, the controller 1618determines whether the gate current is flowing through the gate of oneof the first and second triacs 1510, 1514. Specifically, if thecontroller 1618 is presently driving the first triac 1510 at step 1858,the controller monitors the output of the first current sense circuit1642 of the first gate drive circuit 1612 at step 1860 to determine ifthe gate current is presently flowing through the gate of the firsttriac 1510. If the controller 1618 is presently driving the second triac1514 at step 1858, the controller monitors the output of the secondcurrent sense circuit 1652 of the second gate drive circuit 1616 at step1862 to determine if the gate current is presently flowing through thegate of the second triac 1514. If the gate current is not flowingthrough the gate of the first triac 1510 or the gate of the second triac1514 during the sampling window at step 1864, the controller 1618increments the variable GC_COUNT at step 1866. If the variable GC_COUNTis equal to a maximum number, e.g., two (2), at step 1868, thecontroller executes an ON routine 1880, which will be described ingreater detail below with reference to FIG. 18D. Similar to the OFFroutine 1890, the ON routine 1880 guarantees that the state of thelighting load 1508 as determined by the controller 1618 does not changetoo often by ensuring that the controller 1618 detects that gate currentis not flowing through the gate of the controlled triac for apredetermined number of consecutive half-cycles, e.g., approximatelytwelve (12) consecutive half-cycles, before determining that thelighting load 1508 is on. After executing the ON routine 1880, thecontroller 1618 clears the variables LVD_COUNT and GC_COUNT at step 1852and stops driving the appropriate triac 1510, 1514 at the end of thehalf-cycle at step 1856, before the procedure 1830 exits.

If the gate current is flowing through either of the gates of the triacs1510, 1514 during the sampling window at step 1864 or if the variableGC_COUNT is not equal to two at step 1868, the controller 1618determines whether the AC line voltage has reached the end of thesampling window at step 1870. If not, the controller 1618 waits at step1872 and then samples the LVD control signal and the GC control signalagain, such that the control signals are sampled approximately every 250μsec. If the AC line voltage has reached the end of the sampling windowat step 1870, the controller 1618 executes the OFF routine 1890 andclears the variables LVD_COUNT and GC_COUNT at step 1852, before ceasingto drive the appropriate triac 1510, 1514 at step 1856. Finally, theprocedure 1850 exits.

FIGS. 18D and 18E are simplified flowcharts of the ON routine 1880 andthe OFF routine 1890, respectively, which are both called from thezero-crossing procedure 1830. The controller 1618 uses two variablesON_COUNT and OFF_COUNT to keep track of how many consecutive half-cyclesthat the zero-crossing procedure 1830 has executed the ON routine 1880and the OFF routine 1890, respectively.

During the ON routine 1880, the variable OFF_COUNT is cleared (i.e., setto zero) at step 1882 and the variable ON_COUNT is incremented by one atstep 1884. If the variable ON_COUNT is less than eleven (11) at step1886, the ON routine 1880 simply exits. If the variable ON_COUNT isgreater than eleven, i.e., is twelve (12) or greater, at step 1886, thecontroller 1618 determines that the lighting load 1508 is on at step1888 and the ON routine 1880 exits. In contrast, during the OFF routine1890, the variable ON_COUNT is cleared (i.e., set to zero) at step 1892and the variable OFF_COUNT is incremented by one at step 1894. When thevariable OFF_COUNT is greater than eleven at step 1896, the controller1618 determines that the lighting load 1508 is off at step 1898.

Preferably, the variables LVD_COUNT, GC_COUNT, ON_COUNT, OFF_COUNT usedby the controller 1618 during the zero-crossing procedure 1830 areinitialized to zero during a start-up procedure of the controller 1618.

Upon determining the state of the lighting load 1508 using thezero-crossing procedure 1830, the controller 1618 is able to control thevisual display of the user interface 1528 to provide feedback of thestate of the lighting load 1508 and to report the state of the lightingload 1508 via the communication circuit 1534.

FIG. 19 is a simplified block diagram of a three-way system 1900 thatincludes a smart dimmer 1902 according to a seventh embodiment of thepresent invention. The smart dimmer 1902 includes similar functionalblocks as the smart switch 1602 of FIG. 16A. However, the smart dimmer1902 does not require a neutral connection. Further, the smart dimmer1902 is operable to control the amount of power delivered to thelighting load 1508 to thus control the intensity of the lighting load. Acontroller 1918 controls the triacs 1510, 1514 on a complementary basis,i.e., in a similar manner as the smart dimmer 502 of FIG. 5A, usingforward phase control dimming. A power supply 1920 and a zero-crossingdetector 1926 are coupled across the first and second triacs 1510, 1514via two diodes 1922, 1924, respectively.

As with the smart switch 1602 of FIG. 16A, the controller 1918 isoperable to control the trigger circuit 1640, 1650 of the gate drivecircuits 1612, 1616 to fire the triacs 1510, 1512, respectively. Thecontroller 1918 is also operable to determine if the gate current isflowing in response to the current sense circuits 1642, 1652 of the gatedrive circuit 1612, 1616, respectively. A resistor 1960 is coupledbetween the dimmed hot terminals DH1, DH2 to allow the gate currents toflow through the gate drive circuits 1612, 1616 regardless of theposition of the connected three-way switch 1504.

FIG. 20A is a simplified diagram showing waveforms of the operation ofthe smart dimmer 1902 when the smart dimmer is coupled to the line sideof the system 1900, the controller 1918 is driving the first triac 1510,and the three-way switch 1504 is in position A, such that the lightingload 1508 is on. The gate current for the first triac 1510 flows throughthe AC voltage source 1506, the first triac 1510, the trigger circuit1640, the current sense circuit 1642, the three-way switch 1504, and thelighting load 1508. The controller 1918 renders the triac 1510conductive at a firing time t_(FIRE) each half-cycle depending upon thedesired lighting level of the light load 1508. After the first triac1510 is fired, the gate current flows into the gate of the first triacfor a period of time until the load current through the main terminalsof the first triac exceeds a latching current rating and becomesconductive. The GC control signal generated by the current sense circuit1642 is pulled low to circuit common when the gate current is flowing asshown in FIG. 20A.

FIG. 20B is a simplified diagram showing waveforms of the operation ofthe smart dimmer 1902 when the smart dimmer is coupled to the line sideof the system 1900 and the controller 1918 is driving the first triac1510, but the three-way switch 1504 is in position B, such that thelighting load 1508 is off. Since the three-way switch 1504 is inposition B, the gate current for the first triac 1510 flows through theAC voltage source 1506, the first triac 1510, the trigger circuit 1640,the current sense circuit 1642, the resistor 1960, the three-way switch1504, and the lighting load 1508. The resistor 1960 preferably has aresistance of 110 kΩ, such that the magnitude of the gate current isprevented from exceeding the latching current rating of the triac 1510.Since the first triac 1510 does not become conductive, the gate currentcontinues to flow and has a magnitude greater than zero (i.e., asdetermined by the impedance of the zero-crossing detector 1626) forsubstantially the length of each half-cycle. Accordingly, the GC controlsignal is pulled low to circuit common for the rest of the half-cycleafter the controller 1918 attempts to drive the first triac 1510,signaling that the first triac is not conducting the load current. Theresistance of the resistor 1960 is chosen such that the gate current isgreater than approximately 1 mA and the current sense circuits 1642,1652 pull the GC control signal low when the gate current is flowing.

The controller 1918 is operable to determine the state of the lightingload 1508 in response to the current sense circuits 1642, 1652 of thegate drive circuits 1512, 1516, respectively. After rendering one of thetriacs 1510, 1512 conductive, the controller 1618 checks the GC controlsignal provided by the current sense circuit 1642, 1652 of thecontrolled triac. Preferably, the controller 1918 samples the GC controlsignal at a time t_(SAMPLE) after the controller begins driving thetriac via the appropriate trigger circuit 1640, 1650 as shown in FIGS.20A and 20B. If the gate current is not flowing (i.e., the gate currenthas a magnitude of substantially zero volts and the GC control signal ishigh) at the sampling time t_(SAMPLE), the controller 1918 determinesthat the triac is conducting the load current and the lighting load 1508is on. If the gate current is flowing (i.e., the gate current has amagnitude greater than substantially zero volts and the GC controlsignal is low) at the sampling time tSAMpLE, the controller 1918determines that the controlled triac is not conducting the load currentand the lighting load 1508 is off.

FIG. 21 is a simplified flowchart of a zero-crossing procedure 2100executed by the controller 1918 periodically in response to receiving anindication of a zero-crossing from the zero-crossing detector 1926,i.e., once every half cycle of the AC voltage source 1506. Thecontroller 1918 also executes the button procedure 1800 of FIG. 18Aperiodically, e.g., approximately once every 10 msec, to determine whichof the triacs 1510, 1514 to control. Referring to FIG. 21, when thecontroller 1918 receives an indication of a zero-crossing at step 2110each half-cycle, the controller renders one of the first and secondtriacs 1510, 1514 conductive at the appropriate firing time t_(FIRE)after the zero-crossing. Specifically, if the controller 1918 iscontrolling the first triac 1510 at step 2112, the controller drives thefirst triac at the firing time t_(FIRE) via the first gate drive circuit1612 at step 2114. If the controller 1918 is controlling the secondtriac 1514 at step 2112, the controller drives the second triac at thefiring time t_(FIRE) via the second gate drive circuit 1616 at step2116. The controller 1918 continues to drive the appropriate triac 1510,1514 for a period of time, e.g., 200 μsec, at step 2118.

After the period of time expires at step 2118, the controller 1918checks one of the GC control signals from the current sense circuits1642, 1652 to determine the state of the lighting load 1508. If thecontroller 1918 is controlling the first triac 1510 at step 2120, thecontroller samples the GC control signal of the current sense circuit1642 of the first gate drive circuit 1612 at step 2122. Otherwise, thecontroller 1918 samples the GC control signal of the current sensecircuit 1652 of the second gate drive circuit 1616 at step 2124. If thesample of the appropriate GC control signal shows at step 2126 thatthere is gate current flowing at the sampling time t_(SAMPLE), thecontroller 1918 executes the OFF routine 1880 of FIG. 18E and eventuallydetermines that the lighting load 1508 is off if there is gate currentflowing for twelve consecutive half-cycles. If the gate current is notflowing at step 2126, the controller 1918 executes the ON routine 1880of FIG. 18D and eventually determines that the lighting load 1508 is onif there is not gate current flowing for twelve consecutive half-cycles.Next, the controller 1918 stops driving the appropriate triac 1510, 1514at step 2128 and the procedure 2100 exits.

The smart switches 1502, 1602 could alternatively operate as smartdimmers to provide phase-control dimmed-hot signals to the connectedlighting load 1508 to control the intensity of the lighting load.

The smart dimmers 502, 602, 702, 802, 1902 and smart switches 1502, 1602are useful in three-way and four-way applications without therequirement of replacing the standard switches already installed in theother switching location(s). Unlike applications described above in theprior art, all other switches at other switching locations in the samethree-way or four-way circuit do not have to be replaced with anaccessory dimmer. Accordingly, the present invention has a reduced cost.Only one smart three-way or four-way dimmer or switch need be purchasedand the existing switches in the three-way or four-way switching circuitremain fully operational. By installing a single smart dimmer 502, 602,702, 802, 1902 or smart switch 1502, 1602, less time is required forinstallation, thereby reducing installation costs. Also, there is lesschance of errors in installation (e.g., mistakes in wiring), furtherreducing installation costs and the likelihood of damaging and replacingunits.

Thus, the smart dimmers 502, 602, 702, 802, 1902 and smart switches1502, 1602 are configurable as three-way or four-way (or multi-way)switches that improve upon prior art smart dimmers and smart switches.In accordance with the present invention, the dimmers are relativelyinexpensive to manufacture, and are easier to install in existingelectrical systems than prior art smart dimmers providing three-way andfour-way switching functionality. For example, users are not required toreplace other existing three-way switches with accessory dimmers.Moreover, modifications to wiring of the other existing three-wayswitches is avoided.

Furthermore, the various examples of three-way dimmers 502, 602, and 702illustrated herein are each shown as connected directly to the line-sideof the lighting control systems. One of ordinary skill in the art willrecognize that, in the alternative, the dimmers 502, 602, and 702 couldbe wired on the load-side of the systems.

Although the words “device” and “unit” have been used to describe theelements of the lighting control systems of the present invention, itshould be noted that each “device” and “unit” described herein need notbe fully contained in a single enclosure or structure. For example, thedimmer 502 of FIG. 5 may comprise a plurality of buttons in awall-mounted enclosure and a controller that is included in a separatelocation. Also, one “device” may be contained in another “device”. Forexample, the semiconductor switch (i.e., the controllably conductivedevice) is a part of the dimmer of the present invention.

The present application is also related to commonly-assigned co-pendingU.S. patent application, Attorney Docket No. P/10-980 (07-21335-P2),filed the same day as the present application, entitled LOAD CONTROLDEVICE HAVING A GATE CURRENT SENSING CIRCUIT, the entire disclosure ofwhich is hereby incorporated by reference.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art.Therefore, the present invention should not be limited by the specificdisclosure herein.

1. A load control device adapted to be coupled to a circuit including anAC power source, a load, and a single-pole double-throw three-wayswitch, the AC power source generating an AC line voltage for poweringthe load, the load control device comprising: first, second, and thirdelectrical load terminals; a first controllably conductive device havinga conductive state and a non-conductive state, the first controllablyconductive device electrically coupled between the first load terminaland the second load terminal such that when the first controllablyconductive device is in the conductive state and the load control deviceis coupled to the circuit, a load current is operable to flow betweenthe first load terminal and the second load terminal, the firstcontrollably conductive device having a first control input and operableto enter the conductive state in response to a first gate currentconducted through the first control input; a second controllablyconductive device having a conductive state and a non-conductive state,the second controllably conductive device electrically coupled betweenthe first load terminal and the third load terminal such that when thesecond controllably conductive device is in the conductive state and theload control device is coupled to the circuit, the load current isoperable to flow between the first load terminal and the third loadterminal, the second controllably conductive device having a secondcontrol input and operable to enter the conductive state in response toa second gate current conducted through the second control input; and acontroller operable to control the first and second controllablyconductive devices to control the load between an on state and an offstate, the controller operable to drive the first controllablyconductive device to change the first controllably conductive devicefrom the non-conductive state to the conductive state each half-cycle ofthe AC line voltage, the controller operable to determine, in responseto the magnitude of the first gate current through the first controlinput of the first controllably conductive device, whether the firstcontrollably conductive device is presently conducting current to theload.
 2. The load control device of claim 1, wherein the controller isfurther operable to drive the second controllably conductive device,such that the second controllably conductive device is operable tochange from the non-conductive state to the conductive state, thecontroller operable to determine if the second controllably conductivedevice is presently conducting current to the load in response to themagnitude of the second gate current through the second control input ofthe second controllably conductive device.
 3. The load control device ofclaim 2, further comprising: a first sense circuit having an inputoperatively coupled to the control input of the first controllablyconductive device and an output operatively coupled to the controller,the first sense circuit operable to provide a first control signalrepresentative of the magnitude of the first gate current to thecontroller; and a second sense circuit having an input operativelycoupled to the control input of the second controllably conductivedevice and an output operatively coupled to the controller, the secondsense circuit operable to provide a second control signal representativeof the magnitude of the second gate current to the controller.
 4. Theload control device of claim 3, wherein the controller is operable todetermine that the load is in the on state if one of the first andsecond gate currents has a magnitude of substantially zero amps.
 5. Theload control device of claim 4, wherein the controller is operable todetermine that the load is in the off state if one of the first andsecond gate currents has a magnitude greater than substantially zeroamps.
 6. The load control device of claim 5, wherein the controller isoperable to determine that the load is in the off state if the firstgate current has a magnitude greater than substantially zero amps whenthe controller is driving the first controllably conductive device, andto determine that the load is in the off state if the second gatecurrent has a magnitude greater than substantially zero amps when thecontroller is driving the second controllably conductive device.
 7. Theload control device of claim 6, wherein the controller is operable todetermine that the load is in the off state if the first gate currenthas a magnitude greater than approximately one milliamp when thecontroller is driving the first controllably conductive device, and todetermine that the load is in the off state if the second gate currenthas a magnitude greater than approximately one milliamp when thecontroller is driving the second controllably conductive device.
 8. Theload control device of claim 4, wherein the controller is operable todetermine that the load is in the on state if the first gate current hasa magnitude of substantially zero amps when the controller is drivingthe first controllably conductive device, and to determine that the loadis in the on state if the second gate current has a magnitude ofsubstantially zero amps when the controller is driving the secondcontrollably conductive device.
 9. The load control device of claim 3,further comprising: a line voltage detect circuit operatively coupled tothe first terminal to detect the presence of the AC line voltage at thefirst terminal.
 10. The load control device of claim 9, wherein thecontroller is operable to determine that the load is in the off state ifthe AC line voltage is not present at the first terminal.
 11. The loadcontrol device of claim 10, wherein the controller is operable todetermine that the load is in the on state if one of the first andsecond gate currents has a magnitude of substantially zero amps.
 12. Theload control device of claim 9, further comprising: a neutral terminal;wherein the line voltage detect circuit is coupled between the firstterminal and the neutral terminal.
 13. The load control device of claim3, wherein the first and second sense circuits comprise first and secondcurrent sense circuits.
 14. The load control device of claim 13, furthercomprising: a first trigger circuit coupled in series electricalconnection with the first control input of the first controllablyconductive device and the input of the first sense circuit; and a secondtrigger circuit coupled in series electrical connection with the secondcontrol input of the second controllably conductive device and the inputof the second sense circuit; wherein the first and second triggercircuits are responsive to the controller.
 15. The load control deviceof claim 14, wherein the first and second trigger circuits compriseopto-triacs.
 16. The load control device of claim 13, wherein the firstand second current sense circuits comprise opto-couplers.
 17. The loadcontrol device of claim 3, wherein the controller is operable todetermine that the load is in the on state if the first gate current isnot flowing near the peak of the AC line voltage when the controller isdriving the first controllably conductive device, and to determine thatthe load is in the on state if the second gate current is not flowingnear the peak of the AC line voltage when the controller is driving thefirst controllably conductive device.
 18. The load control device ofclaim 17, wherein the controller is operable to determine that the loadis in the off state if the first gate current is flowing near the peakof the AC line voltage when the controller is driving the firstcontrollably conductive device, and to determine that the load is in theoff state if the second gate current is flowing near the peak of the ACline voltage when the controller is driving the second controllablyconductive device.
 19. The load control device of claim 3, wherein thecontroller is operable to drive the first controllably conductive deviceat a predetermined time each half-cycle, and to monitor the firstcontrol signal from the first sense circuit after a predetermined amountof time has expired since the first controllably conductive device wasdriven by the controller.
 20. The load control device of claim 3,wherein the controller is operable to drive the first controllablyconductive device at substantially the beginning of a half-cycle, and tomonitor the first control signal from the first sense circuit during thehalf-cycle near a time corresponding to a peak voltage of the AC linevoltage.
 21. The load control device of claim 2, further comprising: aneutral terminal; wherein gate current is conducted through the neutralterminal.
 22. The load control device of claim 21, further comprising: afirst zero-crossing detector coupled to between the second terminal andthe neutral terminal; and a second zero-crossing detector coupled tobetween the third terminal and the neutral terminal; wherein the firstgate current is conducted through the first zero-crossing detector tothe neutral terminal, and the second gate current is conducted throughthe second zero-crossing detector to the neutral terminal.
 23. The loadcontrol device of claim 21, further comprising: a power supply coupledbetween the first terminal and the neutral terminal, the power supplyoperable to provide power to the controller.
 24. The load control deviceof claim 2, wherein the first and second controllably conductive devicescomprise bidirectional semiconductor switches.
 25. The load controldevice of claim 24, wherein the bidirectional semiconductor switchescomprise triacs.
 26. The load control device of claim 2, furthercomprising: a communication circuit adapted to transmit a messageincluding feedback information representative of the states of the firstand second controllably conductive devices and the outputs of the firstand second sensing devices.
 27. The load control device of claim 2,further comprising: a visual display for providing feedback to a user ofthe load control device.
 28. The load control device of claim 2, whereinthe controller is operable to drive the first and second controllablyconductive devices a complementary basis, such that when the firstcontrollably conductive device is conductive, the second controllablyconductive device is non-conductive, and when the second controllablyconductive device is conductive, the first controllably conductivedevice is non-conductive.
 29. A method for controlling a load in acircuit comprising a power source, the load, a load control device, anda single-pole double-throw three-way switch, the method comprising thesteps of: providing first, second, and third electrical load terminalson the dimmer switch; electrically coupling a first controllablyconductive device between the first load terminal and the second loadterminal, the first controllably conductive device having a conductivestate and a non-conductive, the first controllably conductive devicearranged such that when the first controllably conductive device is inthe conductive state, a load current is operable to flow between thefirst load terminal and the second load terminal, the first controllablyconductive device having a first control input; conducting a first gatecurrent through the first control input to cause the first controllablyconductive device to enter the conductive state; electrically coupling asecond controllably conductive device between the first load terminaland the third load terminal, the second controllably conductive devicehaving a conductive state and a non-conductive state, the secondcontrollably conductive device arranged such that when the secondcontrollably conductive device is in the conductive state, the loadcurrent is operable to flow between the first load terminal and thethird load terminal, the second controllably conductive device having asecond control input; conducting a second gate current through thesecond control input to cause the second controllably conductive deviceto enter the conductive state; monitoring the first and second gatecurrents; and determining, in response to the step of monitoring thefirst and second gate currents, whether the respective controllablyconductive device is presently conducting the current to the load. 30.The method of claim 29, wherein the step of monitoring further comprisesmonitoring the magnitudes of the first and second gate currents.
 31. Themethod of claim 30, further comprising the steps of: determining thatthe load is in the on state if the gate current presently has amagnitude of substantially zero amps.
 32. The method of claim 31,further comprising the steps of: determining that the load is in the offstate if the gate current presently has a magnitude greater thansubstantially zero amps.
 33. The method of claim 29, further comprisingthe steps of: detecting the presence of a line voltage at the firstterminal; and determining that the load is in the off state in responseto the step of detecting the presence of line voltage.
 34. The method ofclaim 33, further comprising the steps of: determining that the load isin the on state if the gate current presently has a magnitude ofsubstantially zero amps.
 35. The method of claim 29, wherein the step ofconducting a first gate current comprises driving the first controllablyconductive device at a predetermined time during a half-cycle, and thestep of monitoring comprises monitoring the first control signal fromthe first sense circuit after a predetermined amount of time has expiredsince the step of driving the first controllably conductive device. 36.The method of claim 29, wherein the step of conducting a first gatecurrent comprises driving the first controllably conductive device atsubstantially the beginning of a half-cycle, and the step of monitoringcomprises monitoring the first control signal from the first sensecircuit during the half-cycle near a time corresponding to a peakvoltage of the AC line voltage.
 37. The method of claim 29, furthercomprising the step of: transmitting a message including feedbackinformation representative of the states of the first and secondcontrollably conductive devices, the sensed first electricalcharacteristic, and the sensed second electrical characteristic.
 38. Themethod of claim 29, further comprising the step of: providing feedbackto a user of the dimmer switch via a visual display.
 39. A load controlsystem for controlling the amount of power delivered to an electricalload from an AC power source generating an AC line voltage, the loadcontrol system comprising: a single-pole double-throw (SPDT) three-wayswitch comprising a first fixed contact, a second fixed contact, and amovable contact adapted to be coupled to either the power source or theload, the SPDT three-way switch having a first state in which themovable contact is contacting the first fixed contact and a second statein which the movable contact is contacting the second fixed contact; anda load control device comprising: a first load terminal adapted to becoupled to either the power source or the load to which the SPDTthree-way switch is not coupled to; a second load terminal coupled tothe first fixed contact of the SPDT three-way switch; a third loadterminal coupled to the second fixed contact of the SPDT three-wayswitch; a first controllably conductive device having a conductive stateand a non-conductive state, the first controllably conductive devicehaving a first control input and operable to enter the conductive statein response to a first gate current conducted through the first controlinput; a second controllably conductive device having a conductive stateand a non-conductive state, the second controllably conductive devicehaving a second control input and operable to enter the conductive statein response to a second gate current conducted through the secondcontrol input; and a controller operable to control the first and secondcontrollably conductive devices, the controller operable to determine ifthe first controllably conductive device is presently conducting currentto the load in response to the magnitude of the first gate currentthrough the first control input of the first controllably conductivedevice; wherein when the SPDT three-way switch is in the first state,the controller is operable to control the first controllably conductivedevice such that a load current is operable to flow through the secondload terminal when the first controllably conductive device is in theconductive state, and when the SPDT three-way switch is in the secondstate, the controller is operable to control the first controllablyconductive device such that the load current is operable to flow throughthe third load terminal when the controllably conductive device is inthe conductive state; and wherein the controller is operable todetermine, in response to the magnitude of the first gate currentthrough the first control input of the first controllably conductivedevice, whether the first controllably conductive device is presentlyconducting current to the load, the controller further operable todetermine, in response to the magnitude of the second gate currentthrough the second control input of the second controllably conductivedevice, whether the second controllably conductive device is presentlyconducting current to the load.